Composite material has been widely used in the manufacture of advanced aircraft parts due to the advantages of light weight, high strength and integral manufacture, and has become the optimal material for realizing the light weight of aircraft structures. For example, airbus A 350 uses 52% of composite material, which greatly reduces the weight of the aircraft structure and improves the fuel economy of the aircraft. In addition, to ensure that the aircraft can withstand complicated loads such as impact and alternation, a laminated structure composed of the composite material and high-performance metal is often used in supporting and connecting parts of the aircraft. In order to realize connection and assembly of composite parts and laminated structure parts, a series of machining is needed. Hole preparation processing is one of machining methods with the heaviest workload.
However, the composite material is mainly composed of a fiber reinforced phase and a resin matrix phase in a mixed form, presents obvious anisotropy and lamination characteristics at the macro level, and has low interlayer bonding strength. When the composite material is drilled separately, the axial force generated is large, and the constraint effect of inlet and outlet positions is weak. The most outer layers of material are easily pushed apart, resulting in layered damage, and failure to cut fibers, thereby leading to fiber bending, tear, burrs and other damages. Furthermore, in integrated hole preparation of the composite material/the metal hybrid stack material, such an installation mode that the composite material is on the upper side and the metal is on the lower side is often adopted. In this installation mode, the supporting effect of a metal material outlet side is weak, and it is easy to produce burrs. Moreover, in the cutting process, the metal is easy to produce continuous ribbon chips; in the removal process along flutes, metal chips are easy to scratch the composite material on the upper layer, resulting in difficulty to realize high-quality and high-efficiency processing of the hybrid stack structure of the composite material. Therefore, it is urgent to develop independently a cutter that can not only realize the high-quality hole preparation of the composite material but also realize the high-quality hole preparation of the hybrid stack structure of the composite material.
At present, some scholars have researched and developed hole preparation cutters of the composite material and hole preparation cutters of the hybrid stack structure of the composite material. For hole preparation cutters of the composite material, Jia Zhenyuan et al. of Dalian University of Technology has disclosed a “special drill for efficient hole preparation of carbon fiber reinforced polymer/plastic (CFRP)” with a patent application number of 201510408743.7. The patent relates to a double-vertex angle structure drill with tooth-shaped micro blade for hole preparation of the CFRP. Through the double-vertex angle structure of the major cutting edge, the sawtooth structure of the connecting part of the major cutting edge and the minor cutting edge realizes the integrated processing function of drilling, expanding and reaming, and obtains holes with high dimensional precision. However, because the sawtooth structure is located in the cutting edge which is finally cut, it is easy to cause small tear damage at the outlet and the inlet, and reduce the smoothness of the hole wall. A low chisel edge drill is invented by Suzhou Ahno Precision Cutting Tool Technology Co., Ltd. with a patent application number of 201310104178.6. The drill head is provided with two chip removal slots which form two major cutting edges respectively with the intersecting line of a tool back in the axial direction. The patent has the main feature of three centers, with the middle center lower than the centers on both sides. This design gives consideration to both tool strength and centering capability, and the two external centers can effectively scrape the fibers around the hole and reduce burrs. However, when processing high-strength fibers and composite material with low interlayer strength, it is easy to produce tear damage. For the hole preparation tool of the hybrid stack structure of the composite material, Japanese Kawasaki Heavy Industries Ltd. has proposed a composite material/aluminum alloy hybrid stack step drill with thin transverse cutting variation angle in Development of a Dill Bit for CFRP/Aluminum-Alloy Stack: To Improve Flexibility, Economical Efficiency and Work Environment published on. SAE Technical Paper. The tool improves the quality of integrated hole preparation to a certain extent by reducing the single cutting quantity. However, the problem of highly reliable chip breaking of the metal is still not fully considered, resulting in the accumulation of a large number of metal chips and winding on the tool in the process of drilling and further resulting in eccentricity of the tool in the rotary process, thereby seriously affecting the precision of hole preparation and the service life of the tool.